The committee told the FBI a cloud service provider and security research firm alerted the DNC about a fake login page meant to gather usernames and passwords to access the database.

A source in the DNC said it was investigating if anyone was responsible for the attempted hack.

The fake login page was discovered by San Francisco-based security firm Lookout, which does not work for the DNC.

“It was very convincing,” company vice president of intelligence Mike Murray told CNN. “It would have been a very effective attack.”

A link to the fake login page could be sent via email, Murray said.

Bob Lord, the DNC’s security chief, briefed Democrats at an Association of State Democratic Committees meeting in Chicago.

“These threats are serious and that’s why it’s critical that we all work together, but we can’t do this alone. We need the (Trump) administration to take more aggressive steps to protect our voting systems. It is their responsibility to protect our democracy from these types of attacks,” Lord told CNN in a statement.